The challenge that we intend to address in this proposal is the extent to which epigenetic mechanisms contribute to the etiology of asthma in humans. Several lines of evidence support a role for epigenetics in asthma. Asthma, like epigenetic mechanisms, has a non-Mendelian and parent-of-origin pattern of inheritance, is influenced by the environment, and is modified by in utero exposures. Furthermore, the transcription factors that are involved in the development of mature T cells (Th1, Th2, and Tregs), that are critical to the Th2 immune phenotype in asthma, are regulated by epigenetic mechanisms. Although the difference in asthma incidence in developed versus developing countries has previously been attributed to infectious exposures, the mechanisms accounting for these differences have never been fully explained. We have recently demonstrated that in utero dietary supplementation with methyl donors regulates locus-specific DNA methylation and predisposes mice to allergic airway disease by skewing towards a Th2 phenotype. Based on these observations, we hypothesize that epigenetic mechanisms play a fundamental role in the etiology of asthma by modulating the methylation state and transcriptional activity of critical genes that affect immune maturation and lead to the development of asthma. In the proposed project, we intend to use a novel approach to determine the extent to which epigenetic mechanisms contribute to the etiology of asthma in humans (see Figure). We will measure global methylation patterns in a panel of human sibling pairs discordant for asthma (Aim 1), and in airway epithelia and peripheral blood mononuclear cells (PBMCs) obtained from patients with asthma and controls (Aim 2). We will combine these global methylation marks with our knowledge of global methylation patterns in mouse lungs with allergic airway disease, and then confirm these methylation patterns with direct sequencing (Aim 3). We then propose to validate and further characterize these findings in two independent study populations. Using the original discordant sibling pair sample and their parents, we will test whether these targets are imprinted (Aim 4). Using a large, independent sample of asthmatic cases and controls for which extensive environmental and genetic data are available, we will test whether these targets replicate and whether they are influenced by either environmental or genetic factors (Aim 5). Identifying unique epigenetic marks and linking them to other etiologic factors, such as environmental exposures and genetic variants, will transform our understanding of the etiology and pathogenesis of asthma, and lead to more effective approaches to disease prevention and treatment. Derivation Confirmation Validation Aim 1: Discordant Sibling Pairs Aim 2: Airway Epithelia and PBMCs Murine Lung DNA Methylation Aim 3: Confirm Epigenetic Targets Aim 4: Imprinting Aim 5: Case Control